Protective system for furnace crowns



0d 8, 1940- D. l. RoDENBAuGl-l PROTECTIVE SYSTEM FOR FURNACE CROWNS Filed April '7, 1939 3 Sheets-Sheet 2 :SN a .www www# @N SEM@ PROTECTIVE SYSTEM FOR FURNACE CROWNS Filed April '7. 1939 ls sheds-sheet s Patented Oct. 8, 1940 UNITED STATES raoTEc'rivE SYSTEM Foa FURNACE oaowNs Donald I. Rodenbaugh, Zanesville,` Ohio Applitlon April 7, 1939, Serial N0. 266,683

4 Claims.

The invention relates to a protective system for furnace crowns, and particularly to high temperature furnace crowns, which are the most vulnerable.

The under sides of most industrial furnace crowns, in which the crown forms a part of the combustion chamber, are subjected to a positive pressure. 'I'he total positive pressure on the under side of the crown is equal to the furnace atmosphere pressure desired or required for a particular process, plus the buoyancy pressure. The buoyancy pressure of the products of combustion depends on the temperature and the height of-the crown.

The eil'ect of positive pressure on the under side of the crown is to force the furnace atmosphere through the crown. Furnace atmospheres often carry corrosive dusts and vapors, and these are forced through the brickwork and cause its destruction.

Attempts have been made to increase the eiliciency of high temperature furnaces by insulating the crowns, but when insulation is employed burn-outs are particularly bad because then the insulation must be removed and the crown patched.

Another source of high-temperature crown trouble is the dusty surroundings. The dust settles on the crown or crown insulation, and lters into the joints. Very often a reaction occurs between the dustand the crown material, resulting in holes being eaten through I the crown.

The foregoing will illustrate some of the undesirable and dangerous conditions which may arise in the operation of high-temperature industrial furnace crowns.

One of the objects of the present invention is to prevent the burning of holes in the crowns of high-temperature furnaces, due to internal furnace pressure.

Another object of the invention is to make heat insulation of crowns a safe practice by preventing burn-throughs due to internal furnace pressure.

A further object of the invention is to prevent the corrosion and iluxing of crowns by vapors and dusts carried in the furnace at- .mosphere and which ow through the crown by reason of the internal furnace pressure.

Another object of the invention is to overcome the external corrosion of high-temperature furnace crowns, which operate in dusty atmospheres, by preventing the dust from settling on the crown, or on the crown insulation, and filtering into the Joints of the brickwork.

Still another object of the invention is to make possible the reduction or control of crown temperature. y

A further object of the invention is to provide a combination of differential pressure control with crown temperature control.

Various other objects and advantages of the invention will be apparent to those skilled in l0 the art, from the following detailed description, when taken in connection with the accompanying drawings, in which:

Figure 1 is a vertical longitudinal sectional view of a glass furnace equipped with the protective system of the present invention.

Figure 2 is a vertical cross-sectional view thereof.

Figure 3 is a fragmentary sectional view illustrating a slightly modified form.

Figure 4 is a vertical longitudinal sectional view of a glass furnace equipped with a modilied form of lthe protective apparatus.

Figure 5 is a vertical cross-sectional View, taken on line 5 5 of Figure 4; and

Figure 6 is a `vertical longitudinal sectional view of a furnace, illustrating a modified form of the invention.

Referring to the drawings in more detail, and particularly to Figures 1 and 2, numeral I refers to the combustion chamber of the furnace. The furnace illustrated represents a conventional continuous flow furnace for the melting and refining of glass. The invention, however, is in no manner limited to glass furnaces, but is applicable generally to all kinds of industrial high-temperature furnaces. y

The conventional glass furnace comprises a melting portion and a refining portion, between which there is usually provided a bridgewall 2. The details of construction of various types of industrial furnaces are Well known to those versed in the arts, and since they form no part of the invention they have been omitted. Likewise, as the invention resides in a protective system for the'crowns of furnaces, it is deemed unnecessary to illustrate the lower portion of the furnace, which obviously may be of any desired construction.

Numeral 3 refers to a furnace crown, which of course is formed of blocks of refractory material. If desired, the crown may be covered with blocks of insulating material 4. Numeral 5 refers to expansion slots in the crown. These slots are commonly left open until the major 55 portion of the expansion or heating has taken place, whereupon the remaining opening` is packed solid with refractory material.

Extending over the furnace crown, or over the insulating material on the crown, if employed, is a sheet metal hood or covering referred to generally by numeral 6. This sheet metal hood is spaced the desired distance from the crown, or from the insulating material, to form an air space 1.

Of course the ho'od may be of any desired construction,but in the particular form illustrated it is composed of a number of sheet'metal panels 8 of the desired length and width. The panels are bolted together at air tight, or reasonably air tight, joints 9. Numeral I9 refers to the rear panel which seals against the refrac- 'tory material of the crown, and thus closes the rear end of the hood.

In the specific form of the hood illustrated, the front end panel II has a rounded top portion I2. 'I'his front endpanel preferably extends downwardly to the crown support channel I3, to which it may be attached by any desired means. Numeral I4 refers to a panel which is put in place after the furnace has been heated up and normal expansion of the, parts has occurred.

'Ihe side panels are referred to by numeral I5, and these panels also preferably have rounded tops I5, which provide one method of taking care of the hood expansion as it follows the crown expansion. These side panels also preferably extend downwardly to the side crown support channels I1, to which they may be attached.

Any desired means may be employed for spacing the hood from the furnace crown or crown insulation. In the specic embodiment illustrated, metal feet I8 are employed for this pur-l pose.

In accordance with the present invention a pressure is maintained in the air space 1 somewhat greater than the pressure of the furnace atmosphere. For this purpose there is provided a low pressure air supply main I9 leading from any desired source of air under pressure. The supply of air should, of course, be clean. Leading from the main I9 are feeder pipes 29 which distribute the air from the main to the air space 1. v

Numeral 2| refers to a differential pressure gage, which connects with the air space through piping 22, and with the interior of the furnace through piping 23. The particular differential v gage illustrated is of the electric type, and controls a motor 24, which in turn controls a damper 25 in the low pressure air supply main I9. Of course the invention is in no manner limited to any particular gage or any particular damper operating mechanism, and instead of electric operation, compressed air or hydraulic power would be equally satisfactory.

In operation, combustion in the furnace is regulated for satisfactory glass making conditions, and the furnace pressure is adjusted to the proper value by means of the usual air and stack dampers. 'Ihe proper furnace pressure is usually just enough above atmospheric pressure to insure thatcold air is not drawn into the furnace at the glass le'vel. Reference is made to glass because a glass furnace has been shown, and not because the invention is limited to glass furnaces.

If there is maintained above the crown, or above the crown insulation, a pressure greater through piping 22.

than the pressure of the atmosphere below the furnace crown, all of the' undesirable conditions referred to herelnbefore will be eliminated.

The differential pressure gage 2| maintains the desired greater pressure above the crown. The pressure of the furnace atmosphere is preferably taken Just under the crown, and this pressure is composed of the desired' pressure at the glass line plus the buoyancy pressure of the furnace atmosphere. This combined pressure is communicated to the differential pressure gage through piping 23.

The. positive pressure in the air space 1 is communicated to the differential pressure gage The sensitive differential pressure gage is adjusted to maintain a definite positive pressure in the air space 1, above the pressure existing on the under side of the furnace crown, and this pressure above the crown must be suiilcient to prevent any flow of the furnace atmosphere through the crown. On the' other hand, the pressure maintained in the air space should not be so high as to force a detrimental amount of relatively cold air through the crown into the furnace.

In some installations, particularly those in which no crown insulation is employed, it may be desirable to provide means for cooling the sheet metal hood which extends over the entire crown area. This can readily be accomplished by providing apertures of suitable size in the side panels, or elsewhere, so that a small flow of the pressure air will be maintained. These apertures are shown in Figure 3, and are referred to by numeral 26. The total area of these holes should be such that-the air supply line I9 can still provide suillcient air to maintain the required positive pressure in the air space 1.

Any change in the pressure of the furnace atmosphere is immediately transmitted to the dierential pressure gage 2|, and this gage acts at once to reestablish the set differential pressure by throwing the motor 24 in circuit with the power line. The motor thereupon operates the damper 25 to vary the flow of air under pressure through line I9 and branches 29 to the air space 1, until the set dierential is again established. 'Ihe set differential having been reestablished, the gage cuts olf the power supply to the motor, and the damper remains stationary until some unbalance of the set pressures again occurs. In the event a different differential pressure is desirable it is only nece'ssary to adjust the differential pressure gage.

'I'he only material difference between the disclosure of Figures 1 and 2, and the modified form of Figures 4 and 5, resides in the construction of the hood. The parts I, 2, 3, 4, 5, I3, I1, I9, 29, 2|, 22, 23, 24 and 25, are the same as in Figures 1 and 2, and therefore these same reference numerals have been applied to Figures 4 and 5.

Numeral 21 refers generally to the top of the hood, which is spaced the desired distance above the top of the furnace crown to provide an air space 23. 'I'he top of the hood is preferably formed of a number of panels 29 of the desired size. These panels are bolted together at the joints 39. The rear panel which seals on the furnace crown is referred to by numeral 3|. 'Ihe front panel 32 preferably extends downwardly to the crown support channel I3, to whichl it may be. attached by any desired means, and the side panels 33 likewise extend downwardly to the crown support channels I1. Numeral 34 sov refers to a panel which is put in place after the furnace has been heated up and normal expansion of the parts has occurred.

The top of the hood may be supported by any desired means, but in the particular embodiment illustrated adjustable length hook bolts 35 are attached to clips 33 on the top of the hood, and the upper ends of the bolts hook over buckstay tie rods 31 which connect the buckstays 33.

This specific form of hood construction possesses certain advantages. For example, the end panel 32 and side panels 33 are suiiiciently flexible to permit the lower ends thereof to move outwardly during expansion of the crown. Also, the whole -weight of the hood is carried by the steel work of the furnace. Further, the hood does not drag on the crown, or on the crown insulation, when the furnace is heating or cooling. And of course port holes could be provided in the side and end panels, if desired, so that the entire surface of the crown could be inspected.

The mode of operation isr exactly the same as hereinbefore described in connection with the form of construction shown in Figures 1 and 2.

It seems unnecessary to illustrate the invention as applied to a suspended crown, for the construction of suspended crowns is well known, and obviously the invention is adapted to use with suspended crowns as well as with sprung crowns.

As is well known, the bricks in suspended crowns are hung either from individual metal rods or in bundles fastened together by metal hooks. One end of the rod or hook is buried in the outer extremity of the brick and the other end fastens to the supporting steel work.

'I'he furnace pressure causes holes to be burned through-the crown, as hereinbefore described. and once the heat reaches the metal supporting the brick, destruction is very rapid. Also, suspended crowns operating in dusty surroundings are vulnerable because the dust collects on the crown and covers the metal support rods where they enterthe brick. The metal support is thus insulated from its necessary cooling air, and due to the resulting high temperature it eventually fails. 'Ihe cleaning of this type of crown. while in service, is almost impossible because of the multiplicity of support rods or hooks. And when insulation is employed with suspended crowns, great care must be exercised to keep the metal supports open to the atmosphere. The situation is particularly bad in dusty surroundings, for the dust collects between the insulating material and the metal support rods.

Obviously a form of the invention such as illustrated in `Figures 4 and 5 is ideally suited to a suspended crown furnace, in which case the sheet metal hood 21 could be supported on top of the steel work which supports the crown brick.

As mentioned hereinbefore the invention is not limited to any particular crown construction, or to any particular type of furnace, a glass furnace having been selected merely to illustrate one application of the invention.

Whatever the construction of the hood may be, and whatever the type of furnace may be, the broad principle involved consists in maintaining above the crown a pressure somewhat greater than the total positive pressure of the furnace atmosphere below the crown.

By maintaining the proper differential pressure, the furnace atmosphere cannot flow tlirough the crown, or crown insulation, and

consequently burn-throughs which cause the deterioration and eventual destruction of the crown, are avoided. Of course the differential pressure also overcomes the corrosion and fiuxing of crowns caused by vapor or dust carried in the furnace atmosphere, by preventing the furnace atmosphere from owing through the crown.

It will also be apparent that the hood will prevent the accumulation of dust on the top of the crown, or crown insulation, which dust would cause the external corrosion of the high-temperature furnace crowns.

I have disclosed herein means for maintaining the desired difference between the pressure above and below the crown, but in certain processes it is desirable to protect the crown from failure due to high temperatures.

In Figure 6 there is shown a modified form of the invention, by which there is provided a combination of differential control with crown temperature control. For the purpose of illustrating this combined control, I have shown in Figure 6 the same construction, with the same reference numerals, as in Figure l, but I have combined a crown temperature control with such structure. Numeral 39 refers to any desired type of crown temperature measuring device. The device illustrated is of the electric type, and controls a motor 40, which in turn controls a damper 4I located in an air supply by-pass 42 around the damper 25.

'Ihe damper 4i in the by-pass would normally be closed. However, when the crown reachesv a certain pre-set temperature this damper will be opened and remain open. until the crown temperature drops below the set value. When the damper 4I is open, the pressure in the air space 1 may rise enough to cause the differential pressure gage to close the damper 25. When the crown temperature has dropped sufficiently, the by-pass damper 4i will close, the pressure in the, air space 1 will drop, and damper 25 would be opened again as required, by the differential pressure gage. 11n connection with the combined differential pressure and temperature control, the hood would preferably be provided with vents ofsuitable size and number, such as apertures 23.

While I have shown the combined control in connection with the hood construction shown in Figures 1 and 2, 'yet it will be obvious that the combined control is equally well adapted to the form of hood'construction shown in Figures 4 and 5, or to any other suitable form of hood construction. It will also be apparent that the combined control may be used with or without crown insulation.

In certain processes it may be desirable to have two or more separate crown areas, with an independent differential pressure control for each of the areas. And likewise, when there are separate crown areas, it may be desirable to have a combination of differential pressure and crown temperature control for each area.

It will be understood, of course, that the present invention is intended to include all such modifications.

Having fully described the invention, what I claim is:

1. A protective system for furnace crowns, including an air space provided over the crown, an air pressure line leading to said space, a differential pressure gage, means for communicating the air space pressure and the furnace atmosphere pressure to the differential pressure gage,

the furnace atmosphere pressure being derived from a source independent of the air space, and means controlled by said gage to regulate the flow of air under pressure to the air space to maintain a pressure therein greater than the pressure of the furnace atmosphere.

2. A protective system for furnace crowns, including a metal hood spaced above the crown to form-an air space extending over the crown, an

air pressure line leading to said air space, a I

to form an air space extending over the crown. an air pressure iine leading to said air space, means for venting air from-said space to the atmosphere, a diierential pressure gage. said gage communicating with the air space and with the furnace atmosphere, the furnace atmosphere pressure being derived from a source independent oi' the air space, and means controlled by the differential pressure gage for regulating the ow. of air under pressure through said line to the air space.

4. A protective system for furnace crowns, including an air space provided over the crown, means for maintaining the air in said space at a pressure sumcient to prevent the flow of the furnace atmosphere through the crown, and other means controlled by the crown temperature for regulating the ow of air under pressure to the air space.

DONALD I. RODENBAUGH. 

